In Corsica, blue tits bring sprigs of aromatic plants into their nests. But do these plants really protect the chicks from parasites? The answer is not so simple.
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Out of more than 200 plant species in their habitat, blue tits use only about 10, all of them aromatic. In one Corsican population, these plants did not reduce nest infestation by parasites. However, the young grew better and were in better condition when they fledged.
In chicks most heavily infested with larvae of blood-sucking flies, researchers observed changes in the bacterial communities and lower bacterial density. This result comes from a single population and remains debated.
A meta-analysis of 28 experiments on seven bird species shows that fresh nest plants can improve chick body mass and size, but the data do not confirm a reduction in parasites.
In Tunisia, no study has so far been found showing wild birds using plants in this way.
